Strain-wave transmission with tubular strain wheel

ABSTRACT

The strain-wave transmission according to the invention is provided, for purposes of sealing between input and output parts on both sides of the strain-wave generator, with an overlying cup-shaped jacket which is stiffened from within against bulging by a likewise cup-shaped support member open toward the pressure side. For the purpose of sealing, the frontal edges of the strain wheel and of the support members are nonrotatably and sealingly interconnected and the input-side support member is flanged onto the housing cover via a tube. The elimination of a differential pressure in the frontal regions of the strain wheel enables a flexible structure of the support member and an overall lower bulging stress with a more favorable stress distribution, thus allowing the use of more readily deformable wall thicknesses and a more reliable sealing with improved life span.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase application corresponding to PCT/EP83/00148 of June 9, 1983 and based in turn on the German application No.P 32 22 117.7 filed June 11, 1982.

1. Field of the Invention

My present invention relates to a strain-wave transmission which issealable between input and output sides, in particular for a positioningdrive for valve bodies, comprising a strain-wave generator, a deformablestrain wheel with support members, and at least one annular gear.

2. Background of the Invention

German patent 29 44 123 shows a strain-wave transmission in which thedriving and driven shafts are assigned to different pressure spaces,whose strain wheel designed as a cup-shaped case is axially clamped atone end and at its opposite end is provided with a rigid bottom. Axialforces caused by the system pressure, acting on this bottom, must bedissipated via the peripheral surface of the strain wheel, which maylead to bugging and buckling thereof. Depending on the magnitude of theapplied forces, a dependable meshing of the gear teeth is no longerassured or the shell suffers a permanent deformation and thereby becomesuseless. Tests have shown that the cup-shaped case cannot stand aprolonged period of operation. The useful life of a strain wheel soconstructed is short. Although the forces acting laterally on theperipheral surface of the strain wheel are absorbed by support members,compressive forces acting upon the bottom of the strain wheel cannot bedissipated through the rigid support members. The differential pressurethus requires relatively thick walls in the region of the strain wheel,which additionally increases the deformation work of the strain-wavegenerator. Besides, the alternating tension stresses a relatively largesealing collar of the cup-shaped case and thereby impairs the sealingagainst the housing.

OBJECT OF THE INVENTION

The invention has the object of providing a strain-wave transmissionwith excellent sealability constructed to resist higher pressures thanthe known transmission according to the preamble and so to attain ahigher life span.

SUMMARY OF THE INVENTION

According to the invention the problem is solved by the features recitedin the characteristic clause of claim 1.

According to the invention the strain wave transmission has a housingsealable between input and output sides, a strain-wave generatorconnected with a driving shaft, a deformable cylindrical strain wheelmeshing with an annular gear of a driven shaft, the end faces of thestrain wheel surrounding support members whose frontal edges are tightlyconnected with the strain wheel. In this construction:

the support members are open on both end faces and are cup shaped, and

the bottom of the input-side support member is mounted non-rotatably andsealingly on the housing by means of a tube segment surrounding thedriving shaft.

Compared to that which is known, the invention has the advantages thatconsiderably higher system pressures than heretofore can act withoutdetriment upon the strain-wave transmission, and that greater usefullife than heretofore is attainable. Thereby the transmission becomesmore versatile in use and the intervals between repairs aresignificantly prolonged.

The bilaterally cup-shaped, open design of the strain wheel according tothe invention, and of the two support members tightly connectedtherewith at the frontal edge which can be relatively thin-walled inproximity to the edge by virtue of the extensive relief from thedifferential pressure, enables a reduction of the bulging stress, with amuch more uniform stress distribution in the strain wheel and at thesupport members, whereby the danger of rupture from alternating stressesis considerably reduced and comparatively higher pressure loads becomepossible.

It is also advantageous that the connection between the support membersand the housing is now no longer provided via a part of the strain wheelitself but via a considerably thinner tube, between the bottom and thecover of the housing, which is there more reliably sealable by means ofa small sealing flange practically unaffected by the alternate bendingsof the strain wheel.

Owing to the fact that the bottoms of the support members are nowlocated very close to the strain-wave generator and the remaining regionbilaterally absorbs the high pressure, their peripheral region highlystressed by the differential pressure is now comparatively much smalleror shorter and is therefore also much easier to deform mechanically thanwith the cup-shaped case of prior construction subjected over its entirelength to the differential pressure.

According to a further feature of the invention there is provided ateach open end of the strain wheel a respective membrane ring throughwhich the strain wheel is connected with the respective support member.This has the result that the axial deformations additionally caused bythe strain-wave generator in the cylindrical peripheral surface of thestrain wheel, at the frequency of the driving speed, are alsocompensated. Furthermore, the axial flexibility of the membrane ringprevents axial movements of the support members, which are caused bydeformations thereof under the effect of the system pressure or by thecompensation of play due to manufacturing tolerances, from reaching theperipheral surface.

Another feature of the invention provides that the output-side supportmember is braced via a thrust bearing, the strain-wave generator, asecond thrust bearing and the input-side support member. On account ofthe system pressure acting upon both support members, only a part of theaxial forces need to be dissipated via the thrust bearings and thestrain-wave generator.

According to another embodiment of the invention, the support membersare connected with the housing only via a common tube with peripheralopenings through which a driving connection (e.g. planetary-geartransmission, hydraulic motor, electric motor or the like) to thestrain-wave generator is provided.

In a further of this embodiment the tube is designed as a planet carrierin the zone between the two support members, the strain-wave generatorbeing driven via a sun gear and planet gears. The construction of thetube for the connection and mounting of the two support members as aplanet carrier leads to a simplification of this embodiment withuncharged favorable sealing mode.

Strain-wave transmissions with planetary-gear sets are known fromBritish Pat. No. 12 64 590 and German Pat. No. 11 82 011. Both thesetransmissions, however, lack features for a pressure-tight separation ofthe input and output sides, or suggestions for a support capable ofsustaining high differential pressures for the strain wheel which ishere not cup-shaped on both sides.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained for two embodiments with the aid of theaccompanying drawings in which:

FIG. 1 shows in perspective representation, partially in section, thestrain-wave transmission according to the invention with attached motorand a sliding valve body;

FIG. 2 shows a section through the transmission along a line II--II inFIG. 1;

FIG. 3 shows in enlarged representation a cutout of the sectional viewof FIG. 2 with respective parts of the free end of the strain wheel, asupport member and a membrane ring, and;

FIG. 4 shows schematically another embodiment with a tube for holdingboth support members.

SPECIFIC DESCRIPTION

A valve body, e.g. a slider 2 (FIG. 1), is equipped with a positioningdrive 1. The latter is located in a housing, consisting of housing parts3, 4, and has a driving shaft 5 with which a handwheel, a handlever orthe output shaft of an electric motor 22 is fixedly connected to actuatethe positioning drive 1.

In the embodiment the driving shaft is supported on the one hand in thehousing part 3 (FIG. 2) and on the other hand by rollers 18 and 19 eachof which forms a thrust bearing. The strain-wave transmission furthercomprises a strain-wave generator 12, of elliptical periphery as knownper se and fixedly connected with driving shaft 5. It is in turnsurrounded by rollers 17 (FIGS. 1, 2) which are part of a radialbearing.

A support member 10 is fixedly clamped unilaterally in the embodimentbetween the housing parts 3, 4. It is formed as a hollow body with atubular segment 28, a bottom 29 and a sustaining peripheral wall 25, andpartially encloses a space 20. The other support member 11 has a bottom30 as well as a peripheral wall 26. In its bottom 30 an end of drivingshaft 5 can be rotatably journaled.

The two support members 10, 11 carry a strain wheel 7 designed as abilaterally open hollow or sleeve. The latter is tightly connected atits respective open ends to the two support members 10, 11. On the outersurface of the strain wheel 7 there is provided a set of gear teeth 7',which in the embodiment meshes on the one hand with the internaltoothing of an annular gear 16, fixedly mounted in the housing 4, and onthe other hand with the internal toothing of a rotatable annular gear15. The output of the transmission occurs by way of a hollow shaft 14and the driven shaft 6 unitary therewith.

The strain wheel 7, carried by the two support members 10, 11, is weldedat each of its open ends onto a respective membrane ring 8, 9 which inturn is welded in the region of its inner edge to a ring 23 (FIG. 2) ofthe support 10 and a ring 24 (FIGS. 2, 3) of the support 11,respectively. Between the cover 8 and the ring 23 and between the cover9 and the ring 24 (FIG. 3) there is provided a respective gap 27 (FIG.3) which increases the mobility of the strain wheel 7 on the supportmembers 10, 11.

Thus, when the driving shaft 5 is rotated in either direction, in amanner known per se, the strain-wave generator 12 rotates with it andits elliptical outline leads to a deformation of the wall of the strainwheel 7 in the region of the radial bearing formed by the rollers 17.The bulging of the wall of the strain wheel 7 leads to a movement at theends of the strain wheel and thereby to a modification of the width ofthe gap 27 (FIG. 3) between the cover 9 and the ring 24 on the one handas well as between the cover 8 and the ring 23 on the other hand.Because of the large distances in the region of the membranelike covers8, 9, the strain wheel is carried so-to-speak floatingly by the supportmembers 10, 11.

Both spaces 20, 21 are under system pressure. For this reason, theperipheral wall 25 of the support member 10 and the peripheral wall 26of the support member 11 can be made with small wall thickness sincethey have to transmit only the forces acting directly on the peripheralsurface of the strain wheel 7.

The support member 10 fixedly clamped in housing 3, 4 is centered on thedriving shaft 5. The other support member 11 bears upon the housing viaa thrust bearing formed by the rollers 18, the strain-wave generator 12,a further thrust bearing formed by the rollers 19, and the tube segment28.

Another embodiment (FIG. 4) provides that both support members 10, 11bear upon the housing 3, 4 via a common tube 40. The tube 40 is designedin the region between the two support members 10, 11 as a planet carrierfor planetary gears 43 forming the strain-wave generator with ring gear44 driven thereby. A sun gear 41 is fixedly connected with the drivingshaft 5 which is aligned with an axis of symmetry 45 and meshes withgears 43 which extend through slots 40' formed in tube 40 but do notorbit the sun gear. For reasons of simplicity of the graphicrepresentation, FIG. 4 shows only one half of the strain-wavetransmission. In this embodiment the output of the transmission occursvia the deformable ring gear 44, the rollers 17 of the radial bearingand annular gears 15, 16 as well as the hollow shaft 14.

I claim:
 1. A strain-wave transmission comprising:a housing having aninput side and an output side; an input shaft extending axially intosaid housing at said input side; an output shaft extending axially outof the housing at said output side; a tubular deformable cylindricalstrain wheel received in said housing and extending generally coaxialwith respect to said shafts between said sides of said housing, saidstrain wheel having at an intermediate location along its length,gearing respectively engaging gearing on said housing and on said outputshaft; a strain-wave generator carried by said input shaft and disposedat said intermediate location for deforming said strain wheel to effectrotation of said output shaft at a speed different from that of saidinput shaft upon rotation of said input shaft; a first cup-shapedsupport extending from said input side substantially to saidintermediate location within said strain wheel and an end of saidsupport rigidly affixed to a corresponding end of said strain wheel atthe input side without engagement with the housing; and a secondcup-shaped support extending substantially from said intermediatelocaton toward said output side of said housing and having an end atsaid output side rigidly affixed to an end of said strain wheel at saidoutput side, said first support being formed with a transverse bottomremote from its end affixed to said strain wheel and a tube sectionconnected to said bottom, said tube section coaxially surrounding saidinput shaft and affixed at an end of said tube section remote from saidbottom to said housing, each of said supports being open in thedirection of the respective end affixed to said strain wheel, saidsecond support having a transverse bottom remote from its end affixed tosaid strain wheel and guided on said input shaft.
 2. The strain-wavetransmission defined in claim 1 wherein said strain wheel at each ofsaid ends is formed with a respective inwardly extending membrane ring,each of said supports having at the respective end affixed to saidstrain wheel, an inwardly extending flange secured along an inner edgeto a respective inner edge of a respective one of said rings, eachflange and ring having an axial clearance between them outwardly of therespective inner edges.
 3. The strain-wave transmission defined in claim2 wherein said second cup-shaped support bears via a thrust bearing,said strain-wave generator and a further thrust bearing upon saidhousing, said thrust bearings engaging the respective transverse bottomsof said first and second cup-shaped supports and being braced by saidintermediate location against said housing.
 4. The strain-wavetransmission defined in claim 2 wherein said bottoms are connected by acommon tube, said generator being constituted by a pair of planet gearscarried by said tube and a ring gears engaged by said planet gear. 5.The strain-wave transmission defined in claim 4 wherein a sun gearmeshing with said planet gears is carried by said input shafts.